iOS GameCenter connection from different networks - ios

Question

I have made an iOS multiplayer GameCenter game, but right before publishing found an issue I don't know how to solve. In coding process I used Ray Wenderlich tutorial http://www.raywenderlich.com/3276/how-to-make-a-simple-multiplayer-game-with-game-center-tutorial-part-12
GameCenter view controller is shown, connection creates and game can be played until both devices are on the same Wifi network.
If I turn off Wifi on my phone and use 3G network, then try to start new game - in that case connection isn't made anymore. Both devices find each other, but hangs on "Connecting..." screen. It looks like that
- (void)match:(GKMatch *)theMatch player:(NSString *)playerID didChangeState:(GKPlayerConnectionState)state
is not called. Any ideas how to solve it or at least understand, where exactly is the problem?

Answer 1

I think that in your particular case the problem is that your 3G ISP restricts connections from necessary ports. The Apple docs say:
To use Game Center ... port forwarding must be enabled for ports 443 (TCP), 3478-3497 (UDP), 4398 (UDP), 5223 (TCP), 16384-16387 (UDP), and 16393-16472 (UDP)
I faced this issue too when trying to play on iPad connected via bluetooth to iPhone: there was "Connecting..." screen on each device.
But when I use built-in iPad 3G (with a different tariff plan) everything goes fine.
Just remind, in a normal match-making scenario match:player:didChangeState: may not be called. You should also check match.expectedPlayerCount:
- (void)matchmakerViewController:(GKMatchmakerViewController *)viewController didFindMatch:(GKMatch *)theMatch {
//...
if (theMatch.expectedPlayerCount == 0) {
NSLog(#"Ready to start match!");
}
}
Also I expected a similar problem with "Connecting..." screen, but on Wifi network.
And it was reproduced only on iOS6 and after I tried rematch via -[GKMatch rematchWithCompletionHandler:^(GKMatch *match, NSError *error) {}] before.
One device hanged on "Connecting..." screen but on the other matchmakerViewController:didFindMatch: was successfully called, but what is interesting is that match.expectedPlayerCount was 0 and match.playerIDs array was empty at the same time.
I think such error occurred because I tried to find a new match while previous match tried to reconnect on background thread in the same time. And because of that new match was obtained corrupted.
The decision is to wait for rematchCompletion being called and only then try to find new match. There is no interface in GKMatch to cancel rematch, so I use [[GKMatchmaker sharedMatchmaker] cancel] and after several seconds rematchCompletion is called with error and we are ready to start finding new match.
Also I figured out that old unsued GKMatch instances are not deallocated and continue to live somewhere in GameKit framework. And they may probably cause problems if the work with them is not finished correctly (i.e. not disconnected, or rematch is not canceled in my case ). So do not forget to call -[GKMatch disconnect] and finish any other kind of work before removing the last strong reference to the match object .